Belgium and Spain had the most prominent policy errors in their care homes, which led to it's exorbitant high percentages. In Belgium they didn't have enough N95 face masks, so caretakers started sharing them. In Spain it was a similar care home fuckup (Fascist government cuts, they only kept the hospitals in excellent shape). My guess is that the UK with its privatized care homes had similar issues. No idea yet about the high rates in France. They didn't had fascist government lately I thought (Forgot about Sarcozy apparently). Italy had its high flu IFR's of over 1% for decades. (Privatized homes plus high air pollution plus Berlusconi, leading to be the world flu leader). The US has its sugar crisis and healthcare crisis known for decades, besides it's political inefficiency.
Treatment protocol improvements are another theory, but as far as I see it they still use oxygen ventilators, which is known to be of not much help. So unlikely. They also refused to use known therapeutical prevention methods which did work (politics were apparently more important than saving life's of elders), instead promoted fringe methods like 5% face masks and school closings.